The present invention relates to a process for preparing a shrink packaging material. More particularly, the present invention relates to a process for preparing a heat shrinkable film, which has a little variation in thickness and is excellent in transparency and heat shrinkability at low temperature, and which is prepared from a resin composition containing as a main component a copolymer of ethylene and an .alpha.-olefin having a g* value as a parameter indicating straightness of molecular chain of 0.3 to 0.7.
Heretofore known are such heat shrinkable films as polyvinyl chloride films, biaxially stretched polypropylene films, polyethylene films or polyamide films and so on.
Among them, the biaxially stretched polyethylene film has been practically used because of its heat sealability and low cost. Especially, in recent years, a heat shrinkable polyethylene film prepared from a linear low density copolymer of ethylene and an .alpha.-olefin (such copolymer hereinafter referred to as "a linear low density ethylene-.alpha.-olefin copolymer") has become the object of public attention because of its excellent impact resistance and heat sealability.
Among the linear low density ethylene-.alpha.-olefin copolymers, those having a g* value, that is, [.eta.]/[.eta.].sub.L of 0.3 to 0.7 have a good transparency. When preparing the heat shrinkable films therefrom according to a known tubular biaxial stretching method such as the process described in Japanese Examined Patent Publication (Tokkyo Kokoku) No. 36142/1982, in which a tubular film is extruded and biaxially stretched under gas pressure, however, because of an insufficient stretching stability and a large variation in thickness of the obtained film, a practically satisfactory film cannot be obtained.
The present inventors have been studied a process for preparing a heat shrinkable polyethylene film having little variation in thickness and a good heat shrinkability at low temperature, from the above-mentioned linear low density ethylene-.alpha.-olefin copolymer with an excellent transparency. As a result, the present invention has been accomplished.